Alright, we've got some good news...I took a look around in the engine room and was able to locate the captive nuts. They're just behind the headlight assemblies, hidden behind a bunch of brackets and stuff. I can just barely reach them with my finger tips. Its a big nut on top of a loose flat square piece of metal, which is encased within a riveted frame bracket. It looks like perhaps the frame bracket is designed to keep the metal square from spinning all the way around when the bolt is turning. Furthermore, in my case, the nut is separated from the metal square, but I can't see any shearing damage. Also I can move the metal square a few millimeters up and down with my fingertips. I'm not sure what to make of this. I'll know more when I'm able to fiddle with the bolts at home this afternoon.

I attached the best picture I could take in my dark office garage. You can see the red end of the bolt sticking up through the nut. I guess the good news is that its not hidden deep within the frame, necessitating cutting and welding. Its probably completely accessible if you remove the bumper, grille, headlights and a few other bits.

 

Here's a better picture showing the top of the nut and square plate within the bracket. And it looks like that bracket is actually bolted in place, not riveted. Again, this is just lower and behind the high-beam section of the headlight assembly.

I'm happy to see that Jaguar put a little more thought into this on the XJ than they did on the X-type.

 

Ok, so I discovered that the captive nuts are not welded to anything, thankfully. The nut is perfectly secured within the square plate, but they are two separate pieces. The plate is then secured by the bracket, which keeps it from spinning all the way around.

So, that's one disaster averted.

I was able to back the subframe bolt out and retighten to spec. I'm not sure what happened before, maybe I just panicked when I felt it turning too easily (I'm very paranoid about wrecking threads and snapping bolts). So with everything bolted up properly, I can report...that I still have a clunk.

Hell, for now I'm just glad that my fears of having to cut open the frame were not realized. Back to the drawing board...

 

I'm curious about the basis of your issue, rusted subframe bolts. I wouldn't have thought Los Angeles would be the corrosion center of the universe, so where does that leave drivers from Vermont and the Adirondacks? Sitting in the road with cars that have come apart? I thought the rust-outs from the 70's-80's had taught automakers a thing or three about corrosion resistance. Makes me depressed to think about it.

 

I'm afraid you misunderstood. Thankfully there's no rust anywhere on the car, thanks to the dry climate and the aluminium body. I was afraid that the welded nut had just broken free from a combination of age and torque. Thankfully that wasn't the case, as those captive nuts are not welded at all (smart design on Jaguar's part).

 

I put new struts on and still have clunk. New lower control arm front bushings, new upper A arms, new sway bar bushings all to no avail. I've pulled, pushed, lifted, stretched about everything in the front end and can't find where this clunk is coming from. Mine is at slow speed going over the smallest of bumps. It sounds like tie rod ends, but having taken them off and they are as tight as ever.

I am going to find this noise because it has become personal now.


What driving situation causes yours to clunk?

 

Have you checked the sway bar endlinks? To test, remove them and go for a short drive. If the clunk is gone, that's your answer.

 

You haven't yet mentioned the lower air spring bushes. Have you checked these ? I'm on my 2nd X350, an X358 Sovereign, and I can tell you, based on experience with the two cars that the suspension is not quiet, in fact I think Ford, (whose suspension design it is), didn't realise this suspension was going into a luxury up-market car. My wife's New Beetle is quieter !

 

Yes, I have undone both and gone for a drive and the clunk is still there. Thanks for the tip though.

 

Yes, they were checked thoroughly when I put the new air shocks on. I twisted and pulled both of them and they appeared to be in perfect condition. I replaced the lower control arm forward bushings as they were obviously torn and in need of replacement.

There is a limited number of items to be checked, and I feel as if I have checked them all. That is why this is so frustrating.

 

Did you check the balljoints on the vertical arms? Or the big bushing that connects the straight lower arm to the subframe? Unfortunately that one is difficult to check with it still on the car. Both of mine looked fine until I removed them and found they were ripped so badly i could see through them.

 

And also, weren't there a few threads about the air springs themselves becoming noisy and clunking? I know the new Arnott advertise how their upper mount design eliminates clunks.

 

I have checked those ball joints in the past, but will go through everything again next time I have it on the lift. I replaced the large bushings in the lower control arm (see pic), they were both torn completely through. Together we will figure out our respective clunks, there is a definite cause and we will find it.

 

I put new Arnott air springs on the car, thinking that was definitely going to be the cause - but it didn't affect the noise. The air springs needed replacing anyway, so the cost was tempered some when the noise was still present.